We then identified GRN-associated genes, 249 GRN+ and 124 GRN−genes (Table S3), using CCLE data to evaluate how GRN mediates tumor-intrinsic resistance, which are also associated with both primary and acquired chemo-resistance (Fig. S2). When we classified human SCLC tumors by the GRN-associated genes into GRN-high (n = 45) and GRN-low (n = 90) groups (Fig. S3), GRN-low group showed better survival in both Overall Survival (OS) and progression free survival (PFS) with chemotherapy (Fig. 2A), while GRN-high group did not differ in survival with or without chemotherapy (Fig. 2B).

GRN and Its Associated Genes Classify SCLC Patients into Groups with Distinct Therapeutic Responses. A, B KM plots (left: OS and right: PFS) showing survival differences between chemo-treated and not-treated patients in GRN-low group (A) and in GRN-high group (B). Samples from George et al. whose survival information available are included in the analysis. Log rank test (LRT) p-values are calculated to assess survival differences between the groups. C GRN expression (y-axis) in various cell types in SCLC primary tumors. Cell type annotation information is from the original paper [10]. D GRN expression (y-axis) varies in myeloid cells from patients with different disease progression. E UMAP plot showing multiple myeloid subtypes annotated in the original paper [10]. F GRN expression (y-axis) in myeloid subtypes. Expression differences are assessed by Wilcoxon rank-sum test. G–I Cell fractions are estimated in bulk tissue expression profiles of primary tumors for alveolar macrophages 1/2, and tumor-associated macrophages in GRN-high and GRN-low tumors classified based on GRN-associated genes. Two-sided t-test p-values are assessed for cell fraction differences. J–L KM plots showing survival differences between Atezolizumab and placebo in GRN-high, in GRN-mid, and in GRN-high groups for and overall and progression-free survival respectively. Log rank test (LRT) p values are calculated to assess survival differences between the groups

Single-cell RNA-seq analysis of human SCLC tumors [10] revealed that GRN was highly expressed in alveolar macrophages (AMs) and tumor-associated macrophages (TAMs), especially in patients with progressed disease (Fig. 2C–F, Fig. S4). Cellular composition of the bulk SCLC tumors by deconvolution [11] revealed a significant positive correlation between GRN expression and the proportion of macrophages, particularly AM1, AM2, and TAMs (Fig. 2G–I). This suggests that GRN-high tumors have a more macrophage-enriched TME, which may contribute to both chemo-resistance and immunotherapy resistance.

Given these results, we explored whether GRN could serve as a biomarker for predicting immunotherapy response. Analysis of 271 treatment-naive patients from the IMpower133 clinical trial data [12], which combined chemotherapy with ICB (anti-PD-L1), showed that patients with GRN-high and GRN-mid tumors did not benefit from additional immunotherapy (Fig. 2J, K). In contrast, patients with GRN-low tumors showed a significant survival benefit from the combination of chemotherapy and immunotherapy (Fig. 2L). This differential response supports the potential of GRN as a stratification biomarker for ICB therapy response.